To minimize the adverse effects of polarization aberrations in the projection optical system, methods to compensate the
polarization aberrations are required for high resolution lithography. In this paper, we propose a symmetric polarization
aberration compensation method based on scalar aberration control for lithographic projection lens. This method focuses
on the compensation of polarization aberrations induced by radially symmetric retardances. The foundation of the
compensation method is the linear relationship between conventional even aberration and polarization aberration induced
by radially symmetric retardances. The compensation accuracy is dependent on the even aberration adjustment accuracy
of the projection lens and the sensitivity of the mask pattern to even aberrations. By this polarization aberration
compensation method, the lithographic process window can be improved obviously.

This paper proposes an analytical model to describe the mask diffraction in EUV lithography. The model is used to
improve the understanding of the EUV mask performance and to analyze relevant mask topography effects. The
multilayer and absorber constituting the EUV mask are simulated separately in this model. The light incident on the
mask is first diffracted by the absorber, and then reflected by the multilayer and propagated upwards through the
absorber again. The multilayer reflection is calculated by a mirror approximation, and the absorber transmission is
calculated by a modified Kirchhoff model, where the absorber is considered to be thin and located in a certain plane.
Moreover, an analytical expression of the diffraction spectrum of masks with arbitrary pattern orientation is derived.
Comparisons with rigorous simulation are used to validate the accuracy of the developed model. It predicts mask
diffraction of 16nm wide line and space features. For 0.35 NA EUV systems with an incidence angle of 6° the simulated
CD errors are below 0.5 nm, with a pattern pitch ranging from 32nm to 250nm.

We propose a novel method of one-shot parallel complex Fourier-domain optical coherence tomography using a spatial carrier frequency for full range imaging. The spatial carrier frequency is introduced into the 2-D spectral interferogram in the lateral direction by using a tilted reference wavefront. This spatial-carrier-contained 2-D spectral interferogram is recorded with one shot of a 2-D CCD camera, and is Fourier-transformed in the lateral direction to obtain a 2-D complex spectral interferogram by a spatial-carrier technique. A full-range tomogram is reconstructed from the 2-D complex spectral interferogram. The principle of this method is confirmed by cross-sectional imaging of a glass slip object.

In a conventional sinusoidal phase-modulating laser-diode (SPM-LD) interferometer, the wavelength of LD is sinusoidally modulated by varying its injection current. However, the intensity modulation is associated with wavelength modulation, which affects the measurement accuracy. We propose here a method to eliminate the effect of intensity modulation by choosing appropriate modulation depth for sinusoidal phase modulation in a SPM-LD interferometer. The method is verified by computer simulation and experiment for real-time displacement measurement. The measurement accuracy has been improved and the measurement repeatability is less than 1 nm.

High-speed full-range complex Fourier domain optical coherence tomography (FDOCT) using sinusoidal phase-modulating interferometry is proposed. A high-rate two-dimensional (2-D) CCD camera is used to record time-sequential sinusoidally phase-modulated 2-D spectral interferograms, from which the complex 2-D spectral interferograms corresponding to each frame of the 2-D CCD camera are extracted by Fourier transform method. By taking inverse Fourier transform of the complex spectral interferograms, full-range B-scan images free of the complex conjugate ambiguity as well as dc and autocorrelation noises are obtained at intervals of the frame period of the 2-D CCD camera. Time-sequential cross-sectional imaging of human skin ex vivo with the proposed method is demonstrated.

We propose a technique for dynamic full-range Fourier-domain optical coherence tomography by using sinusoidal phase-modulating interferometry, where both the full-range structural information and depth-resolved dynamic information are obtained. A novel frequency-domain filtering algorithm is proposed to reconstruct a time-dependent complex spectral interferogram from the sinusoidally phase-modulated interferogram detected with a high-rate CCD camera. By taking the amplitude and phase of the inverse Fourier transform of the complex spectral interferogram, a time-dependent full-range cross-sectional image and depth-resolved displacement are obtained. Displacement of a sinusoidally vibrating glass cover slip behind a fixed glass cover slip is measured with subwavelength sensitivity to demonstrate the depth-resolved dynamic imaging capability of our system.

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Advanced PhotonicsJournal of Applied Remote SensingJournal of Astronomical Telescopes Instruments and SystemsJournal of Biomedical OpticsJournal of Electronic ImagingJournal of Medical ImagingJournal of Micro/Nanolithography, MEMS, and MOEMSJournal of NanophotonicsJournal of Photonics for EnergyNeurophotonicsOptical EngineeringSPIE Reviews